Switching direct current (DC) to DC voltage converters are used in a variety of applications for converting power at an input voltage into power at a desired output voltage. Such voltage converters are used to power loads such as battery chargers, computers, televisions, and many other electronic devices.
A voltage converter may step down or step up an input voltage by a fixed conversion factor (e.g., 2:1, 4:1, 1:3) for applications in which the voltage converter's load does not require regulation. Switched-capacitor converters (SCCs) represent a class of voltage converters that may convert voltages based upon such a fixed conversion factor. SCCs operate with low impedance and high efficiency, at least as compared with many other voltage converter types including typical regulated voltage converters. SCCs do not require bulky magnetics (e.g., inductors or transformers), leading to potentially high power density for SCCs. Furthermore, the switch control for SCCs is fairly simple, especially when compared with regulated voltage converters, and does not require measurement sensors as typically needed by controllers for regulated voltage converters.
A typical SCC operates by using switches to transfer energy among several link capacitors. The switches and link capacitors may be partitioned into first and second groups, and a switching cycle of the SCC may be partitioned into first and second phase intervals. During the first phase of a switching interval, the first group of switches conduct such that charge is transferred to the first group of capacitors from the input or from the second group of capacitors. During the second phase of the switching interval, the second group of switches conduct, such that charge (energy) is transferred from the first group of capacitors to the second group of capacitors and to the output and its associated output capacitor. Power flows from the input to the output of the SCC via these energy transfers between the first and second groups of capacitors that occur during the first and second phases of a switching interval.
An SCC's link capacitors must be sized such that they can store the charge that is provided within the first and second phases of the switching interval, with minimal losses during the charge transfers. Furthermore, the output capacitor must be sized such that any voltage ripple at the SCC output is within an acceptable range. These requirements lead to capacitors having fairly high capacitances, and associated large sizes, such that the capacitors comprise a significant portion of the area (and volume) consumed by an SCC.
Circuit topologies and associated techniques that reduce the size of capacitors within SCCs are desired.